The present invention relates to an electromechanical thermal protection relay comprising in a case, components such as thermally deformable bimetal strips in the case of overcurrent in power current lines, as well as switch contacts associated with power lines and able to be actuated by a command element which may be stressed through deformable components.
Usually, the command element acts on a middle point of a thin and flexible blade which has a foot fixed or resting on the case and a head cooperating with a contact maneuvering component. In response to the displacement of the control element resulting from an overcurrent, the stress to which the blade is subject at its middle point causes a sudden displacement of the head from a stable rest position to a working stable position, whereas the foot of the blade substantially remains in its initial position. The blade is designed, made and mounted in order to be able to bow from one stable position to the other, i.e. able to suddenly flex and for this purpose, it has, in its middle portion and for forming an application range for the control element, a protruding finger in a cutout area.
A relay of this type is described in document FR-1 274 608. The prestressing required for bowing the blade is then produced by stiffly fixing and tightening legs provided at the foot of the blade. This embodiment is difficult to reproduce and does not allow the positions of the head to be adjusted.
Another thermal relay of this type is described in document EP-360 215. The prestressing required for bowing the blade is then produced by a bridge of material embossed in the foot of the blade, whereas a stiff support, which may be pivotally applied on a support and stressed by an adjustment screw, is fixed at the foot of the blade. The making of the embossed bridge is particularly difficult to reproduce industrially. Further, the overall dimensions of the blade are observed to be too large in height. Finally the device is not satisfactory since, as the prop of the support is located away in height from the area where the control element is applied on the finger of the blade, it causes, a misadjustment of the control element during an adjustment operation made by means of the screw.
The object of the invention is to find a remedy to the aforementioned drawbacks and to make the manufacturing characteristics reliable and reproducible, notably the adjustment conditions for a thermal relay of the described type, while providing it with small dimensions.
According to the invention, the foot of the flexible blade has a folded back extension so as to be applied elastically against a span of the case in order to cause the blade to be pressed against the prop.
The extension may notably extend from the foot of the blade in the direction of its length and be folded, beyond the area for fixing the stiff support on the blade, into the shape of a V or U with respect to the main plane of the blade, wherein the free leg of the V or the U is applied against the span of the case. When the blade is symmetrical, the extension may comprise two symmetrical legs.
Preferably, the pivoting rest point of the support of the blade is located along the length of the blade, substantially at the level of the area of application of the control element on the blade.
The adjustment element may have a cam applied on the stiff support of the blade on the side of the pivoting rest point, wherein this cam is able to rotate around an axis parallel to the main plane of the blade.